Phenotypic and genetic correlations among floral traits in two species of Thalictrum

The evolution of dioecy in plants is expected to be followed by sex-specifi c selection, leading to sexual dimorphism. The extent of the response to se lection depends on the genetic covariance structure between traits both wit hin and between the sexes. Here I describe an investigation to determine ph enotypic and genetic correlations between reproductive traits within crypti cally dioecious Thalictrum pubescens and within morphologically dioecious T . dioicum. Females of T. pubescens produce flowers having stamens and pisti ls, appearing hermaphroditic. Genetic correlations were estimated as family -mean correlations among paternal half-sib families. Positive phenotypic an d genetic correlations between parts of the same reproductive organs, as th e anther and filament of the stamen, indicate developmental associations be tween these traits in both species. Negative genetic correlations were dete cted between pistil number and size of reproductive organs in T. dioicum an d showed the same direction, but not significance, in T. pubescens. There w as a negative phenotypic correlation between the number of stamens and the number of pistils within female flowers of T. pubescens. Within T. pubescen s, there was a positive genetic correlation between the number of stamens i n males and the number of pistils in females, indicating that floral evolut ion in males and females may not be independent in this species.